When does a Cisco router generate a source quench?

Prior to Cisco IOS Software Releases 11.3 and 12.0, a Cisco router generates a source quench only if it does not have the buffer space needed to queue the packet. If the router can’t queue the routed packet onto the output interface’s queue, it generates a source quench and registers an output drop against the output interface. If the router isn’t congested, it won’t generate a source quench.

You can look at the show ip traffic command output for source quenches sent. Also look at show interface to see if there are any drops. If there are none, then you should not see any source quench.

Cisco IOS Software Releases later than 11.3 and 12.0 do not include the source quench feature.